A recent development in third generation (3G) wireless communications is the long term evolution (LTE) cellular communication standard, sometimes referred to as 4th generation (4G) systems. Both of these technologies are compliant with third generation partnership project (3GPP™) standards. It is anticipated that 4G systems will be deployed in existing spectral allocations owned by Network Operators and new spectral allocations that are yet to be licensed. Irrespective of whether these LTE spectral allocations use existing second generation (2G) or 3G allocations being re-farmed for fourth generation (4G) systems, or new spectral allocations for existing mobile communications, they will be primarily paired spectrum for frequency division duplex (FDD) operation.
In addition to the large number of standard wireless subscriber communication units that employ the above technologies, there is an increasing number of other communication devices that may usefully connect to current mobile telecommunication networks. Examples include so-called machine type communication (MTC) devices, which are typified by semi-autonomous or autonomous wireless communication units that are designed to communicate small amounts of data on a relatively infrequent basis. Examples of MTC devices include so-called smart meters, which, for example, may be located in a customer's house and periodically transmit information back to a central MTC server data relating to the customers consumption of a utility such as gas, water, electricity, and so on. Thus, a large number of MTC devices are expected to support very low power consumption and with small, intermittent data transmissions.
It is also known that ‘uplink-only relaying’ is a network topology that may be used to address the issue of achieving low transmit power in low-cost MTC devices, for instance, in macro cellular LTE networks. In general, in relay-node applications, there is typically sufficient system gain on the downlink (base station to subscriber communication unit or terminal device) to support MTC devices (or User Equipment UE) (MTC-UE) at the cell edge of the macrocell of the eNodeB (eNB). However, with the low output power of the MTC devices the uplink (terminal device to base station) system gain is significantly reduced compared with the downlink. The use of a single hop uplink-only relay device (MTC-RN) can be used to address this issue and close the link budget for MTC-UE. A single hop may be assumed, provided that the MTC-RN can be expected to have similar characteristics to an LTE UE. In a network where relay devices (also referred to herein as relay devices) are utilised to relay uplink data from the terminal devices to the eNodeB, the eNodeB may be referred to as a donor eNodeB (DeNB).
FIG. 1 illustrates a simplified schematic of an uplink-only single-hop relay communication system 100, comprising base station (such as eNodeB) 105, carrier network 110, relay device 115 and user equipment (UE) 120. In this simplified schematic, eNodeB 105 communicates with other eNodeBs (not shown) via the carrier network 110. Communication system 100 comprises an asymmetric uplink/downlink arrangement, whereby wireless downlink communications between the base station 105 and UE 120 have a direct communication path 125, but are single-hopped for the uplink communication path 130 from UE 120 to base station 105 via relay device 115. The base station 110 may also transmit control signalling on a separate downlink path 135 to relay device 115 in order to control the operation of the relay device 115.
The configuration of FIG. 1 allows lower power transmissions to be sent from the UE 120, for example where the lower power is sufficient for the MTC device's lower transmit power to be able to reach the relay device's receiver at a decodeable power level, whereas the MTC device's lower transmit power would not be able to reach the eNodeB's receiver at a decodeable power level. However, the disadvantage with this system is that the transmission time from the UE 120 to the base station 110 has been increased due to the implementation of relay device 115. Further, there is no transmission from the relay device 115 to the UE 120. Therefore, a potential problem with uplink-only relaying is that the relay device is unable to feed back control information to the MTC device to support efficient future transmissions between the MTC device and the base station via the relay device, for example to control the power of such transmissions to avoid interference with other users.
Therefore there is a need for a terminal device and a base station supporting an uplink-only relaying system to be able to better control communications between the terminal device, such as an MTC device, and the base station, such as an eNodeB.